The major objective CETSOL is to improve and validate the modelling of Columnar-Equiaxed Transition (CET) and of the grain microstructure in solidification processing. This aims to give industry confidence in the reliability of the numerical tools introduced in their integrated numerical models of casting, and their relationship. To achieve this goal, intensive deepening of the quantitative characterization of the basic physical phenomena that, from the microscopic to the macroscopic scales, govern microstructure formation and CET will be pursued. This endeavor will be based on the benchmark data obtained from systematic series of critical experiments under diffusive conditions (critical experiments under convective conditions), with fluid flow in the melt due to natural buoyancy-driven convection (convection controlled by applying an external field, magnetic field or vibration).